It would be a very good feature to be able to have kind of a "negative" Advanced Lookup Filter. This would be useful for example to exclude already added records (e.g. Installed Products already added as Covered Products to a maintenance plan could be excluded in the lookup-dialog enabling users to identify not covered products in a fast and simple manner).
What is the underlying problem do you intend to solve with this idea?
Be able to identify "missing" records easily. Avoid double recordings of records.
How is the problem being addressed today, if at all?
Identifying already linked records via reports and or related lists.
Installed Base Management Parts Management Preventive Maintenance Returns Management & Depot Repair Work Order Management